1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt with a material, on the driving surfaces thereof, to suppress noise normally generated by impact and relative movement between the belt and a cooperating pulley.
2. Background Art
Raw edged V-belts, V-ribbed belts, and other types of belts on which a plurality of V-shapes extend longitudinally of the belt, are used in a variety of different environments to transmit up to relatively large forces. These belts have V-shaped ribs with compression sections having surfaces that engage facing pulley surfaces defining receptive grooves for the ribs. Some of the salient features of, and problems with, the above belts will be discussed below.
V-ribbed belts are generally thinner than a conventional V-belt. Resultingly, these belts are quite flexible and can be wrapped around relatively small diameter pulleys to enable a compact overall system to be designed. The flexibility of this type of belt contributes to overall system energy savings. Further increased energy savings and prolonged life are attributable to the way in which the V-ribbed belt cooperates with the pulleys about which it is trained. The individual ribs do not move into the cooperating pulley grooves as deeply as does the rib on a conventional V-belt. The result is that there are less frictional losses as the ribs enter into and come out of the pulley groove, and less tension decay on the belt during operation. This adds considerably to the life of the belt and has made such belts highly useful in many diverse environments, including, for example, the automotive, agricultural and domestic electric implement fields.
One drawback of V-ribbed belts is that in environments in which excessive load is applied to the belts, the belts may slip easily relative to the cooperating pulleys. The slippage may cause excessive and/or uneven wear, cracking, chunking of rib rubber, etc., which shortens the belt life.
Another problem with V-ribbed belts, as well as other types of transmission belts, is the problem of noise generation. Belt noise in a transmission system results from several different causes. First, there is noise that is generated between the belt and pulley, as the belt slips circumferentially with respect to the pulley, as when the belt is operated under high load/high torque conditions. Stick-slip noise is also generated between the belt and pulley and results from relative radial movement between the belt and pulley as the belt is engaged in and disengaged from the pulley.
This latter problem is caused by pulley vibrations self-excited by the belt, particularly at start-up. Oscillatory vibration is a phenomenon in which the belt is rubbed against the pulley under a constant frequency of vibration, with the resulting vibrations being converted to noise resulting when the frequency of belt vibrations are tuned to the natural frequency of the pulley. This problem is most prominent at start-up. This problem results from the increased tension that is applied to the belt at start-up. Once the system is in normal operation, typically the belt tension is dropped to 40 to 50% of that which it was at start-up. Once tension decay occurs, the noise is naturally eliminated.
Various methods have been devised by prior art designers to minimize noise generation, which is a problem encountered in virtually all systems in which there are cooperating ribs and grooved pulleys. One proposed solution has been to cover the driving/driven surfaces of the belt with cloth. This method results in improved noise suppression and improves the wear resistance of the rubber defining the driving/driven surfaces of the belt. However, the drawback with this method is that it is inherently difficult during manufacture to apply the cloth to the rib surfaces. This problem is particularly vexatious with a small rib construction. Still further, the cloth to some degree minimizes the flexibility of the belt. The cloth may fail before the end of the normal anticipated life of the belt without the cloth.
Another proposed solution to the noise generation problem has been to blow short staple reinforcing fibers against the exposed driving/driven surfaces of the belt. While the fibers are easier to apply than a cloth layer, the fibers dispersed on the surfaces of the belt tend to readily fall off the belt, particularly in high torque systems. The result may be an irregular disposition of the fibers on the surfaces, which alters the operating characteristics of the belt and compromises its noise suppression capability. The bending characteristics of the belt may also be altered which may decrease the useful life thereof.
A third method of suppressing noise generation is to embed a canvas layer in the belt ribs. The principal drawback with this construction is that the belt manufacture is difficult and requires a high degree of skill. Manufacture is particularly a problem when the ribs are small.